Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities
Net loss	$ (27,754)	$ (28,323)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense	2,144	234
Depreciation and amortization	886	700
Stock-based compensation	2,936	2,386
Changes in operating assets and liabilities
Purchased premiums and interest on available-for-sale securities	(1)	(291)
Accounts receivable	(6,298)	(531)
Accounts payable, accrued expenses and other	(4,549)	6,910
Deferred revenues	(1,838)	(3,065)
Other assets and liabilities, net	3,087	784
Net cash used in operating activities	(31,387)	(21,196)
Cash flows from investing activities
Purchases of available-for-sale securities	(5,100)	(7,090)
Proceeds from maturities of available-for-sale securities	37,602	20,950
Purchases of property and equipment	(1,438)	(2,354)
Net cash provided by investing activities	31,064	11,506
Cash flows from financing activities
Proceeds from exercise of common stock options and warrants	2,134	199
Other financing activities, net		212
Net cash provided by financing activities	2,134	411
Net increase (decrease) in cash and cash equivalents	1,811	(9,279)
Cash and cash equivalents, beginning of period	65,086	37,714
Cash and cash equivalents, end of period	66,897	28,435
Non-cash investing and financing activities
Issuance of derivative liability		35
Changes in property and equipment in accounts payable and accrued expenses		(662)
Disposal of fully depreciated assets	409	50
Supplemental disclosure of cash flows
Cash paid for interest	$ 3,836	$ 998